Controllable reactance



Oct. 14, 1947.

CLARK ET AL coNTRLLABLE REACTANCE Filed April -30. 1943 llllll S00E05 OFMooumrnvG INVEN 0R3 ROBE/PT W LARK FRANK J SOMERS- A TTOPNEY.

Patented ()ct. 14, 1947 "Robert "were fsomers Newlfork, N.

orporation or America, a corporation of 'DelaiClark, Teaneck, N QL, "andFrank 3.

'e si ne s .Bad

Application-April 30, 1943, senamo. assure scams. (cr me-i715 Thisapplication concerns-reactanceof the tube type and control means forcontrolling the size of the said reactance, :Ina'n application thereactance -is in an oscillation generating circuit or in-atuned-circuit;Means is ,provided to control the said reactance and thereby controlthe "tuning of the generator circuit or tuned circuit to control thetiming oi the oscillatory energy in the generating --circuit iortunedcircui-tr An object of our invention is to improve the operation ofreactance tube circuits of the type -:described above in general. A morespecific object is to improve such systems 'whenthe oscillationsgenerated or flowing in the tuned circuit Y are=of large amplitude. Thevoltage 'fed to the reactance tube control grid in phase quadrature :15derived from the cathodecircuit of a cathode follower type stage. Theamplitude o'ith'e'voltage on the cathode circuit of the cathode followertypestage will be less than that on the "grid and the yoltage on thecathode circuit may be ad;- justed to the desired amount. Thusanimproved means for regulating the quadrature voltage for .bestoperation is-provided.

Another 'obiect of the-present invention is to reduce the "efi-ectsof-regeneration in the reactance tube, say for example, in case -areactance tube of the triode type is used. Since the grid *of thereactance tube derives "the quadrature voltage from the cathodeimpedance cfa stage of the cathode follower type and the cathode toground impedance of such a stage is generally of a low value,regeneration effiects in the reactan'ce tube are reduced.

In addition the modulation amplifier feeding into the grid of thereactancetube, which is also connected to the cathode impedanceof theoathode followerstage; is feeding into a lovv'im-pedance load and thesystem is particularly useful in case a; Wide band oimodulation'frequencies"are used, such as, for example, video or similarsignals.

In'our system -the-control of the tube reactan'ce may "be in accordancewith control potentials 'suchas used in automatic frequency controlsysterns or in accordance with modulating potentials of any type. It isespecially useful where the modulating :potentials extend over a widerange of frequencies. The'c'ontr'ollable reactance may be used tocontrol 'or modulate the phase orfreque'n-cy =o'r the phasean'direquen'cyof wave energy.

Throughout the specification and claims the terin timingm'odulation'will be used and is intendypes of'phase and freed to covertheyarious quncy"modulationormodified formsthereoi.

In describing our-invention in d'etailrefer'ence will be :made' to thedrawings wherein the "single figure illustrates tube and circuitarrangement wherein a controllable capacity "is'developed"bewherei-n-oscil'latory energy flows.

tween the electrodesofthetubein a new and improved manner andusedin-a-nove1 manner to control the timing of oscillatory energy, 7 In the=drawings, l0 is an oscillation generator having itsfirst and seco dgrids and cathode regeneratively coupled-in 'a tuned circuit comprisingcapacity ;C -and inductance L, [The mode of operation of this-typegenerator is believed well :lcnownanda=detai1ed-stateme t thereof isbelieved unnecessary. W The generator is, however,ofthe-regenerative'type -and 9f the electron coupledtype -Inthegene-rator the second gridacts -as-an :anpd-aand the cathodeisinair-rtai ned above ground alternating current potential by thecholeing-inductance +2. oscillation generating BlGGtIOdGSffiI'ECdU-Plfidsubstantially by the electronstreamonly in the tube to the outputcircuit i e e e th n l l. l, a

y The tube 20 ;has itsanode to cathode internal impedance-in shunt 't'oL and C and in this tube the reactive eijfectis developed. The reactiveeffect is across -the circuit LG and as aconsequence determines the reactance thereof and the timfing lo f the pscillationsgenerated inay be atuned circuit wherein an alternating current is induced ratherthanthetanl; of a generator. :The-Qhigh-patntial endoi and L and the anode12 of tube 20 are 'coupled to' thefirsjt grid 24 of an amplifiertube'fslso that the phase ofthe alternating current-potentialbn the"first grid?! oftube ZB and on the anode '52 of tube 20 andentheniginpdteuua1 end of c ircuitLC is the 's'ame. 'The'tubefz't of theca thode follower type having in its cathode groundcircuit a resistancepotentiometer 30. hlpfoint on this resistance poten-tiorneter is coupledby resistance 3| to the contra-1' grid "to provide :the required gridbias in tl i i stubeg; The amount o f the voltage developed inth'ebathode 'c'ir'cu' -is determined by the re- "s'istlan cetn -typeoftube 26, and-the voltage on grid 24. The "potential drop across thepotentiometer; is supplied to aphase shifting networkipcludingresistance R and condenser C l. BI is the-grid-resistorfortube 28- andnormally --is large "in-comparison with Ranol may be disregarded inconsidering the phase shifting network. However, where RI is small it:must be taken into accountwhen"considering the phase shifting network.The common terminals of resistance Band Cl are connectedto the controlgrid -32 of tube 20 The -resisto-r-34, shuntedby radio and-modulationfrequency bypass condenser 35, provides the bias tor the control grid oftube 20.

-In my --system,-dur-ing operation the;alternating current potential atthepathode-end-of resistance =30 varies "in-phase with the alternatingcurrent -:potential"suppIied'-to "the grid 24 of tube 26, andin thearrangement this alternating current potential is of the same Tphas'e'a's the alternating our- '60 rent potentialonte-anode -22 of tube '20.The

3 resistance R and condenser CI provide a phase shifting network bymeans of which the alternating voltage fed to the grid 32 from thepotentiometer resistance 30 is shifted about 90 in phase so that in thetube 20 we have a phase quadrature relation between the high frequencyvoltages on the anode 22 and grid 32. In other words, in this tube 28the current to theanode is 90 out of phase with respect to the anodevoltage and the tube instead of being an amplifier, simulates a reactiveefiect which is reflected into the tank circuit CL. If the current tothe anode leads the anode voltage the reactive efiect which is complexis essentially capacitive. If the current to the anode lags the anodevoltage the complex reactance is essentially inductive.

In an arrangement shown B, Cl and RI (BI is large and neglecting thecapacity of cathode 31 to ground) are dimensioned so that the phase ofthe voltage on the grid 32 is in quadrature with the voltage on theanode 253. In the arrangement shown the resistance of R is made large ascompared to the reactance of Cl so that the current through the circuitis largely resistive and is in phase with the voltage. The reactancedrop across the condenser Cl is 90 out of phase with the current, 1. e.,lags the current by about 90 so that the voltage on the control grid 32lags the voltage on the anode 22 by about 90 and the reactive effect isinductive. If BI is small so that the reactive drop across Cl is not 90out of phase (less than 90) with the current in the condenser Cl aninductance L2 is added to the phase shifting network say in series WlthRor in series with RI. This inductance then retards the current andcauses the current to lag the Voltage an amount sufficient to bring thereactance drop across CI to about a phase quadrature relation withrespect to the voltage at the oathode of tube 26. V

The capacity to ground of cathode 31 may be of such value as to createan appreciable phase angle between the voltage on grid 24 and thevoltage on cathode 31. This phase angle can be corrected by connectingan inductance in series or parallel with resistor 30. The value of thisinductance is such that at the mean frequency of the generatedoscillations it will resonate with the capacity to ground of cathode 37.

By modulating an electrode in tube 28 in accordance with control ormodulating potentials the tube conductance is varied, thereby varyingthe size of the reactive efiect and changing the tuning of the circuitCL. The controlling or modulating potentialsmay be applied to tube 29.In a particular application a video amplifier tube 46 has its outputelectrodes coupled by a video peaking choke LX and loading resistance LRto the control grid 32 of tube 20. This connection includes a radiofrequency blocking circuit in the form of an inductance Ly which withits distributed capacity is parallel tuned to the center frequency atwhich the oscillator tube or tuned circuit LC is operating.

Considerable advantage is derived from the use of my novel arrangementwhere it is desirable or necessary to use a triode tube reactance at 2!]or where a relatively strong oscillation generator is used oroscillations of considerable amplitude are set up in tank LC.

Where a reactance tube of the triode type is used at 20 the anode 22 togrid 32 feed-back inherent in such tubes is minimized by the lowimpedance of the output circuit of tube 26.

The phase shifting network may have the posi- I, ductance instead oftions of R and Cl, reversed so the reactive effect across the circuit LCwill be capacitive, or the network may be composed of a resistance andina resistance and capacitance.

The quadrature voltage on the grid 32 of tube 20 most favorable for itsoperation may be obtained by dimensioning the potentiometer 30. Thus ifthe oscillations in tank circuit LC are strong, tube 26 may be used asan electronic at- ;enuator to produce the required voltage on grid Weclaim:

1. In a tube reactance of controllable reactive value, two terminalsacross which alternating voltages appear and across which a reactiveeffeet is to be produced, a first tube having output electrodesincluding a cathode coupled to said terminals, said tube having acontrol electrode, a second tube having input electrodes coupled to saidterminals, said second tube having a cathode connected by an impedanceto the cathode of said first tube, a phase shifting circuit couplingsaid impedance to the control electrode of said first tube, whereby areactive effect is produced in said first tube, and connections forcontrolling the conductance of said first tube to thereby control theproduced reactive effect.

2. In a tube reactance of controllable reactive value, a tuned circuitwherein alternating current flows and across which a controllablereactive effect is to be produced, a first tube having an anode and acathode coupled in shunt to a part, at least, of said first circuit,said tube having a control electrode, a second tube having inputelectrodes coupled to said first circuit, said second tube having acathode connected by an impedance to the cathode of said first tube, aphase shifting circuit coupling said impedance to the input electrodesof said first tube, whereby a reactive effect is produced in said firsttube and reflected in said circuit and connections for modulating theconductance of said first tube in accordance with control potentials tovary said reactive effect.

3. ma timing modulation system, a tuned circuit wherein alternatingcurrent fiows and across which a variable reactive effect is to beproduced, a first tube having output electrodes including a cathodecoupled in shunt to a part, at least, of said circuit, said tube havinga control electrode, a second tube having input electrodes coupled tosaid first circuit, said second tube having a cathode connected by animpedance to the cathode of said first tube, a phase shifting circuitcoupling said impedance to the control electrode of said first tube,whereby a reactive efiect is produced in said first tube and connectionsfor modulating the conductance of said first tube in accordance withsignals to control said reactive effect and thereby correspondinglymodulate the timing of said alternating current.

4. In a timing modulation system, a tuned circuit wherein alternatingcurrent fiows and across which a variable reactive effect is to beproduced, a first tube, a control electrode having an anode and acathode coupled in shunt to a part, at least, of said circuit, wherebyalternating voltage of a first phase is set up on said anode, a secondtube having a control electrode coupled to the anode of said first tube,said second tube having a cathode, an impedance connecting said lastnamed cathode to the cathode of said first tube, a phase shiftingnetwork circuit coupling said impedance to the control electrode of saidfirst tube, whereby a voltage is set up on said last named electrodewhich is about 90 displaced in phase relative to the phase of thevoltage on the anode of said first tube and a reactive efiect isproduced in said first tube and added to said tuned circuit andconnections for modulating the conductance of said first tube inaccordance with signals to control said reactive effect and therebycorrespondingly modulate the timing of said alternating current.

5. In a simulated controllable reactance, an electron discharge tubehaving an anode, a cathode and a control grid and means for applyingalternating current voltages substantially in phase quadrature upon theanode and control grid of the tube and for varying the tubes gain bycontrol potentials to produce a variable reactive efiect between theelectrodes of said tube comprising, an additional tube having an anode,a cathode and an electron flow control electrode, a coupling forapplying said alternating current to said electron fiow controlelectrode, an impedance coupling the cathode of said additional tube toground, a source of potential connected with the anode of saidadditional tube, a phase shifting circuit coupling said impedance to thecontrol grid of said first tube, said phase shifting circuit includingbetween said impedance and the control grid of said first tube a secondimpedance and between the said control grid and cathode of said firsttube a condenser, and means for controlling the transconductance of saidfirst tube in accordance with control potentials.

6. In a wave frequency control system an electron discharge tube havingan anode, a cathode and a control grid, a tuned circuit whereinalternating current the timing of which is to be controlled fiows, meansfor applying alternating cur- 6 rent voltages from said tuned circuitsubstantially in phase quadrature on the anode and control grid and forvarying the tubes gain by control potentials to produce, a variablereactive effect between the electrodes of said tube to vary thereactance of the said tuned circuit and thereby the timing of saidvoltages comprising, an additional tube having an anode, a cathode and acontrol electrode, a coupling between the control electrode of saidadditional tube and said tuned circuit, an impedance coupling thecathode of said additional tube to ground, a source of potentialconnected with the anode of said additional tube, a phase shiftingcircuit coupling said impedance to the control grid of said first tube,said phase shifting circuit including between said impedance and saidcontrol grid of the first tube an inductance and a second impedance andbetween the control grid and cathode of said first tube a condenser, asource of video signals and an amplifier tube having input electrodescoupled to said source of video signals and having output electrodescoupled to a load and to the control grid of said first tube.

ROBERT W. CLARK. FRANK J. SOMERS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Name Mathes Crosby Roberts Brailsford Number

